Speaking at the White House, Obama said the unprecedented carbon dioxide limits are the "the single most important step" America has ever taken to fight climate change, while warning that the problem was so large hat the world must get it right quickly or it may become impossible to reverse.

"There is such a thing as being too late when it comes to climate change," Obama said. The final version of Obama's plan imposes stricter carbon dioxide limits on states than was previously expected: a 32 percent cut by 2030, compared with 2005 levels, the White House said. Obama's proposed version last year called only for a 30 percent cut.

US President Barack Obama delivers remarks at a Clean Power Plan event at the White House in Washington, DC, August 3, 2015

It also gives states an additional two years — until 2022 — to comply, yielding to complaints that the original deadline was too soon. States will also have an additional year to submit their implementation plans to Washington.

Obama was joined in the East Room by Environmental Protection Agency Administrator Gina McCarthy and by parents of asthma patients. The Obama administration has sought to draw a connection between climate change and increased respiratory illness in vulnerable populations. "This is an especially wicked-cool moment," said McCarthy, wielding a colloquialism from her hometown of Boston.

The pollution controls form the core of Obama's ambitious and controversial plan to drastically reduce overall US emissions, as he works to secure a legacy on fighting global warming. Yet it will be up to Obama's successor to implement his plan, which has attracted strong opposition from the field of Republican presidential candidates.

Opponents announced immediately that they will sue the government, and will ask the courts to put the rule on hold while their legal challenges play out. Many Republican governors have said their states simply won't comply.

Today’s release of the #CleanPowerPlan demonstrates @POTUS’ dedication to solving the climate crisis and is a crucial step on the road (1/2)

The Obama administration estimated the emissions limits will cost $8.4 billion (£5.3 billion) annually by 2030. The actual price won't be clear until states decide how they'll reach their targets. But energy industry advocates said the revision makes Obama's mandate even more burdensome, costly and difficult to achieve.

Commenting on President Obama’s clean energy plan, Friends of the Earth’s chief executive Craig Bennett called the initiative "politically significant," but said it falls "way short of what scientists say is required to tackle catastrophic climate change."

“In the face of huge US vested interests that oppose any measures on climate change, the President’s plan at least pushes the issue up the agenda," he said in a statement.

"But these measures are just a drop in the ocean, when a sea change in energy policy is what’s desperately required. It would have been more significant if the President said no to drilling in the Arctic, and stopped his support for new fossil fuels such as fracking and tar sands,” Bennett added.

Obama climate initiative politically significant, but long way short of what's needed: